The Eco Well's Guide to Bath Bomb Making

Bath bombs are one of my favorite products to use and make. They can be incredibly affordable and require only a little time. With that said, despite my love of bath bombs, they have also been some of the more finicky products I’ve made. Bath bombs that crack, are too soft, don’t fizz, and more, are very common issues many DIY enthusiasts frequently experience. As a result, the below article will be a brief guide to getting started, including some important tidbits about the ingredients you chose to make your bath bomb and problems you may experience, to make your bath bomb making experience way more enjoyable :).


Basic ingredients to make a Bath Bomb


2 parts baking soda

1 part citric acid

A splash of moisture

Mold of choice


Directions:


  1. Mix all of the dry ingredients well in a large bowl before adding a splash of moisture (about ½-3 tsp depending on your batch size)
  2. Pack your mixture into your mold of choice. You can either unmold right away (or after 10-20 seconds) and make multiple bath bombs with a single mold or leave the mixture in the mold to dry.
  3. Wait 12-24 hours for your bath bombs to dry before using them or wrapping them up for a gift.

 

Image from Milky Way, a bath bomb and soap mold supplier.

Optional add in’s


1-2 parts salt of choice: Options here include Epsom salt (not actually a salt and very rich in magnesium), dead sea salt (another magnesium rich ingredient), sea salt, Himalayan salt, etc. While magnesium rich ingredients are great for muscle soothing baths, they also are a bit trickier to work with compared to sea salts since they tend to absorb more water - too much Epsom or dead sea salt, especially if you have slightly too much moisture in your mixture or are working in higher humidity, may cause your bath bombs to fizz out (the citric acid react prematurely), leaving your bath bombs soft, crumbly and not fizzy once they hit the bathtub. If you opt for either of these salts, consider using less moisture, not using water, and perhaps even adding your hydrating ingredient of choice to them, waiting 10-20 minutes before mixing in the rest of your ingredients. If you live in a very low humidity environment (or have a dehumidifier), you less likely to have these problems with magnesium-rich ingredients.

A few tbsps of clay: Great natural color additives and can also give the bath bombs a smoother look. If you’re struggling with too much moisture in your bath bombs, clay can also help dry the mixture out a bit to prevent premature citric acid reactions. Note, a little bit goes a long way, too much will result in bath bombs that are next to impossible to unmold without cracking and possibly crumbly if you do end up successfully taking them out of the mold. Click here for more information about different clay options.

Other color additives of choice: There are so many color additives to chose from, but for bath bomb making, I think botanical options are excellent easy and eco-friendly ingredients to turn to. These ingredients include beetroot for a red to pink color, turmeric for a yellow, spirulina or other greens for a green, etc. Be careful with the amount you add it, too much may stain your tub. Note, I’ve seen activated charcoal become a pretty popular color additive (mostly added for it’s touted health effects)... I would probably not do this in any amount because this ingredient will definitely stain your tub!

Essential Oils: These are great natural aroma options for your bath bombs and also give some additional benefits, e.g. lavender after a stressful day, citrus as a morning energizer, eucalyptus for congestion. When you're using essential oils, be sure to dilute them to 3% (read this article for more information on that), use a carrier oil (this will make them safer for your skin and will also help prevent early evaporation), and make sure the essential oils you're using are safe for your skin and the user (e.g. don’t use cinnamon bark period, I would also consider not using, for example, eucalyptus essential oils (or others rich in 1-8, cineole) for young children). Note, some essential oils may add a bit of color to your bath bomb mix.

Herbs, flowers, other botanicals: These are great for decorating your bath bombs! You can either intersperse these ingredients all throughout the mix or place them at the bottom of your molds (a small pinch) before you pack your mixture and mold. I personally love the look of tea, rose petals, calendula and pink Himalayan salt on the tips of bath bombs.

1 part cornstarch or arrowroot powder: These ingredients will help you achieve a smoother looking bath bomb. If you're struggling with the moisture level in your bath bombs, both of these ingredients will also help absorb some of the mixtures. If you’re using a mechanical bath bomb press, I would consider not using these ingredients. For an unknown reason to me, these ingredients have only given me a hard time with this type of bath bomb mold but not with the hand-mold options (see below).


Note, this is by no means the limit for the add-in options, but for ‘natural’ ingredients, this is most of them! If you have any other add-ins you like to use, tell us about them in the comments below!

 

What kind of ‘moisture’ should you use?


Typically, you can hydrate your bath bombs with any of the following ingredients: water, witch hazel, oil and/or alcohol. The amount of moisture you incorporate into your batch depends, in addition to your batch size, a lot on the type of liquid you use, as they all have slightly different effects. Bath bombs are notoriously finicky and this is a big reason why, but knowing a bit more about each of the ingredients can make your life a lot easier when making these products


  • Water: The trickiest of the hydrating ingredients. Since water evaporates very slowly compared to the ingredients with alcohol (includes witch hazel), the margin of error is a lot smaller. As a result, a wee bit too much water will cause your bath bombs to fizz out, which may take a few hours. If you put way too much water right from the start, you may get a bit of a volcano effect in your bowl and will have to start from scratch again. I would personally recommend not using water.
  • Oil: If you're using essential oil in your bath bombs, you should definitely use at least a little bit of carrier oil. This will make the essential oil a lot safer for your skin and also help prevent the essential oils from evaporating too early. I tend to prefer using rice bran oil, although most carrier oils will work. I find that olive oil is by far the hardest carrier oil to use for me in bath bombs, probably due to how heavy this oil is comparatively. Butters can be added into your bath bombs as well (i.e. shea or cocoa butter), but keep in mind, they’ll be going down the bathtub drain and may not be the nicest for your plumbing.
  • Witch Hazel or Alcohol: Witch hazel is my go-to for bath bombs. Because witch hazel is usually an extract in an alcohol, it evaporates much quicker than water and is significantly easier to use. I also find that having witch hazel in my recipes instead of water helps the bath bombs unmold a lot easier instead of sticking to the molds and pulling each side apart. Many bath bomb makers choose to use rubbing alcohol instead of witch hazel… rubbing alcohol is by far the easiest ingredient to use to hydrate your bath bombs since it barely reacts with the citric acid and evaporates even faster. As a result, you can have a wetter mixture, which will be much easier to pack and unmold, that won’t cause the fizzing out you’d get with water and even witch hazel. If you chose to use rubbing alcohol, your mixture will smell like that ingredient until the bath bomb dries and the alcohol has evaporated.

Note, I would consider using a spray bottle for the water, witch hazel or alcohol for ease of use and less risk of over-hydrating your bath bomb mix.


Note, if you live in a very humid environment, you may not even need to add water or witch hazel, especially if you're using an ingredient rich in magnesium. A dehumidifier may also be a good idea.


What type of mold should you use?


There are so many mold options out there for bath bombs. The most popular are the two-part spherical molds, which often come in either plastic or stainless steel. If you’re planning on making multiple bath bombs in a sitting with a hand mold option, I would opt for the stainless steel since it’s way easier to unmold and a lot more sturdy compared to plastic molds. Flexible silicone molds can be nice, especially if you want to make cute shapes out of your bath bombs. If you use these molds, I wouldn’t bother trying to unmold your bath bombs until they’re dry… unless you're an expert bath bomb unmolder… You can also use just about any jar to make your bath bombs. When I first started making bath bombs, I used to make them in shallow coffee cups… press the mixture in, and then flip the cup over to slowly tap the bath bomb out of the cup. While this is definitely not the easiest method, you can still make really lovely bath bombs like this if you have the patience or touch... If you're interested in making a significant bath bomb investment, you could also consider buying a mechanical bath bomb press. Here’s the one that I use, which I really like, but there are a lot more on the market :).

 

Possible Problems and Solutions


  • Bath bombs that crack: It’s possible that you added slightly too much water, causing the bath bomb to expand as it dried. If your bath bomb cracked or crumbled before dry (e.g. sitting on a table or upon unmold), you may not have enough moisture. Note, witch hazel or rubbing alcohol will make your life easier!
  • Bath bombs that are too soft: You’ve likely added too much oil or used too heavy of an oil, for example, olive oil. Alternatively, too much water or witch hazel, too humid of an environment, or the last two reasons plus the addition of magnesium-rich ingredients (e.g. Epsom salt)  can also do this, often with a slight fizzing out effect. Try putting more dry ingredients, such as more baking soda. You may also want to try incorporating some clay or cornstarch to absorb some of the moisture.
  • Bath bombs that aren’t fizzing: A few things could have gone wrong here. You’ve either put too much water or witch hazel or may have too humid of an environment, which may have reacted prematurely with the citric acid, or added too little citric acid. Alternatively, corn starch or too much oil in the mixture can also reduce the frizziness.
  • Bath bombs are sticking to the mold: This could be due to a few things. If you’re using water, I would definitely consider switching over to witch hazel or rubbing alcohol, as they make the unmolding process a lot easier. You also may not have enough moisture in your mixture, causing the bath bombs not to pack well enough. Finally, if you're still having problems, you may want to also consider the baking soda you're using. While the differences among baking soda are slim, I’ve found that Arm and Hammer baking soda is by far the easiest baking soda option to use.  

Image from Primal Elements

Note, when your bath bombs are dry, store them in a covered container, for example, like a cookie jar or baggie. Opt for packaging that won’t absorb moisture, e.g. cardboard or wood. This will help keep the aroma of your essential oils intact and prevent them from evaporating.